Microclimate Modification with Plasticulture

The climate of the Canadian Prairies can make the production of warm season vegetable crops difficult. Early season soil and air temperatures are cool, slowing plant growth. This places limitations on growers, restricting them to varieties that will mature in a shorter time period. This results in a trade-off in overall quality and yield.

It is essentially impossible to modify a climatic area, other than by placing the whole growing system under cover. The modification of the environment around the roots and shoots of developing seedlings (microclimate) can extend the growing season slightly and provide many benefits, both in terms of yields and quality. Microclimate modification can be accomplished through the use of plastic mulches, mini-tunnels or floating row covers. Warm season crops respond the best to these practices.

Plastic Mulches

Plastic mulches are laid on a prepared soil surface that is free from trash and anchored using the weight of the soil on the edges. Mulch should be laid tightly, to ensure good heat transfer and prevent flapping and movement in the wind. Movement may cause the plastic to tear, eliminating the benefits. Plastic mulches are often used in conjunction with drip irrigation.

Photo Credit: Robert Spencer

.Physical Benefits of Plastic Mulch

Increased soil temperatures (degree depends on mulch type)

Reduced levels of weeds (depending on mulch type)

Reduction in contact with soil and decay organisms

Conserve soil moisture (less evaporation)

Disadvantages of Plastic Mulch

Plastic must be removed and disposed of

Greater initial costs

An increased level of management is required

Plastic mulches come in a variety of colours, with a range of qualities for each type.

The use of coloured mulches may improve fruit yield and quality of some vegetable crops, although results are variable

Mini Tunnels and Floating Row Covers

Mini tunnels involve the placement of plastic or spun-bonded fabric sheets on metal hoops over the developing crop, resulting in a mini-greenhouse effect. Plastic is usually clear and may be solid or perforated. This cover is left on for 3-4 weeks, depending on the crop. Mini tunnels are often used in conjunction with plastic mulches and drip irrigation.

Photo Credit: Robert Spencer

Photo Credit: Robert Spencer

Benefits of Mini tunnels

Increased daytime air temperatures can enhance the growth rates of crops

Perforated covers can reduce the level of manual labour required for ventilation, but do not hold temperatures for as long as solid plastic

Covers can protect crops from insect pests

Spun-bonded fabric will allow passage of rain and irrigation

Disadvantages of Mini tunnels

High daytime temperatures in the spring can result in excessively high tunnel temperatures, impacting flower development and plant survival

Labour intensive to install

May require a lot of labour to ventilate

Can form a barrier to pollinating insects &/or precipitation (solid plastic)

Floating Row Covers are very large sheets of spun-bonded fabric (range of thicknesses available) that “float” over or lie on the developing crop. The material is anchored on the edges with soil, sandbags or rocks. Crops may be direct seeded or transplanted.

Photo Credit: Robert Spencer

Benefits of Floating Row Covers

Do not impede seedling emergence while increasing plant growth through soil and air temperature increases

Rain or irrigation can pass through the fabric freely

Finer weaves can prevent entry of some insect pests

Can provide some frost protection in the fall and spring

Disadvantages of Floating Row Covers

Movement in wind can damage some crops

High winds can be problematic

Cover must be removed to allow entry of pollinating insects = lots of labour